Commodore 64C doesn't work!

[pjmiranda]

Hello everyone!

After some years of inactivity I want resurrect my Commodore 64 (my first computer), in 1996 crashed, and so far has been in a box, although some unsuccessful attempts of arrangement.
But this time I really have to repair the large C64 and relive good old times...
The symptoms are:

- The LED light on;
- Black screen;
- Cassette player does not work.

After reading some posts probably the problem is these chips: U27 (74LS08 ), U14 (74LS258 ) or U31 (74LS629 ).
My board is a PCB ASSY No. 250469 / 25311 Rev.3 and I can´t find these chips on board,
Which chips are down, after all?
Thank you for your help!

 

[channelmaniac]

First... check the +5v to the chips. If bad, replace power supply.

Next, swap out the PLA chip. It's the most common culprit.

If that's not it, it's a crapshoot on several different chips - CIA for keyboard/joystick, CPU, Kernel ROM, or DRAM.

Raymond

 

[pjmiranda]

First... check the +5v to the chips. If bad, replace power supply.

Next, swap out the PLA chip. It's the most common culprit.

If that's not it, it's a crapshoot on several different chips - CIA for keyboard/joystick, CPU, Kernel ROM, or DRAM.

Raymond

Hello Raymond,

First and foremost I am a novice in such matters but here goes ...
I've been measuring the volt chip ( U8 PLA ) was 4.8 V, I think the problem will not be on this chip.
However the chip U6 was only 0.81 V is that the problem is this?
What other chips could be? U7 or U19 for example?
I am open to suggestions.

Thanks for the help.

 

[geoffm3]

What pins were you probing and on what chips? I agree with channelmaniac... PLAs are usually a good place to start with dead/flakey C-64s.